Many search engine services, such as Google, Yahoo!, and MSN, provide for searching for information that is accessible via the Internet. These search engine services allow users to search for web pages and other Internet-accessible resources that may be of interest to users. After a user submits a search request that includes search terms, the search engine service identifies web pages that may be related to those search terms. The collection of web pages that most closely match the search terms is referred to as the “search result.” The search engine service then ranks the web pages of the search result based on the closeness of each match, web page popularity (e.g., Google's page ranking), and so on. The search engine service then displays to the user links to those information sources in an order that is based on their rankings.
Some search engine services do not charge a fee to the providers of web pages for including links to their web pages in search results. Rather, the search engine services obtain revenue by placing advertisements along with search results. These paid-for advertisements are commonly referred to as “sponsored links,” “sponsored matches,” or “paid-for search results.” A vendor who wants to place an advertisement along with certain search results provides a search engine service with a creative and search terms. When a search request is received, the search engine service identifies the advertisements whose search terms match those of the search request. The search engine service then may display some of the advertisements along with the search results.